Internal combustion engines are known to include exhaust gas recirculation (EGR) systems to reduce NOx (nitrous oxide) emissions. Air enters the engine through a turbocharger via a compressor, which pressurizes the air. The pressurized air flows to an intake manifold and enters the cylinders of the engine. The compressor is coupled to a turbine, which is driven by exhaust gas from the cylinders. The exhaust gas from the cylinders enters an exhaust manifold and flows into the turbine. The exhaust gas exits the turbine and is vented to the atmosphere. A fraction of the exhaust gas is diverted from entering the turbine and routed back to the intake manifold. The resultant air charge to the cylinders contains both fresh air and combusted exhaust gas.
In order to achieve the desired exhaust gas flow through the EGR system and into the intake manifold, the pressure in the exhaust manifold must be higher than the (boost) pressure in the intake manifold. In addition, effective use of an EGR system provides a minimum air-to-fuel ratio for relatively clean, smokeless combustion to occur. In conditions where air-to-fuel ratio is favorable for EGR utilization, it is desirable to maximize EGR flow in order to lower NOx emissions. Unsuitable use of EGR systems may result in poor engine performance, including inadequate air-fuel ratio, air flow instability, fluctuating engine speed, engine stumbling, white and black smoke, and/or noise.
Accordingly, there is a need for an EGR system that provides effective air-to-fuel ratio to reduce poor engine performance.